1. Field of the Invention
The present invention relates to a process and a device for producing thin metal bars, especially steel bars, in which an elongated metal product is brought into contact with a molten metal causing the latter to crystallize. The device includes a metallurgical vessel with a bottom opening that holds the molten metal, through which the elongated metal product is conducted, and rollers for conducting the elongated metal product and for extracting the crystallized metal bar.
2. Description of the Related Art
Thin metal steel bars are usually produced as cold strip. Currently, approximately 60% of cold strip products are coated, particularly to avoid or reduce the corrosion of the steel during its use. In the European Union, this volume amounts to approximately 30 million tons of steel, of which 16 million tons consist of hot-galvanized or electro-galvanized strip. In recent years, the production volume of galvanized strip, especially for use in the automotive industry, has increased steadily. At the same time, the scarce zinc resources, are sufficient only for approximately 20 to 30 years, assuming the current production quantities and developed and known reserves. The recycling of zinc requires separate collection of galvanized steel scrap as well as recovery via the dust phase and enrichment, e.g., during melting in an electric furnace.
An alternative to the use of galvanized steel sheet in automobile construction is offered by aluminum sheet. The use of aluminum can similarly improve the corrosion behavior of a chassis and increase the useful life of the units. However, the use of aluminum, due to its characteristic material properties, leads to considerably higher expense in the areas of chassis deformation, joining and paintwork. Equally disadvantageous are the high production costs, especially the high energy costs, starting with aluminum, as long as primary aluminum is needed for the chassis. The aluminum-producing industry is pursuing a long-term strategy of shifting primary aluminum production out of Europe, due to energy and environmental problems. At the same time, however, the production of aluminum cold strip from secondary aluminum is itself problematic. In particular, the problem of impurities has not yet been solved.
In addition to the aforementioned solutions, a massive sheet of stainless steel can also be used. In this case, however, the high raw material costs must be noted, because large quantities of chrome and nickel alloy are required; in addition, processing must be carried out in cold strip mills specially designed for alloyed steels. For market-related reasons, a greater use of stainless steel in automobile construction, though highly desirable from the environmental point of view, has not yet occurred.
To produce thin metal bars with thicknesses less than 20 mm, especially steel bars, inversion casting is known. For example, European reference EP 0311602 B1 proposes a process and device in which an uncooled cleaned elongated metal product of low potential energy is brought into contact with a molten metal, and the latter crystallizes. An economical and metallurgically useful product is attained by virtue of the fact that an elongated metal product with selected wall thicknesses from 0.1 to 1.4 mm, in keeping with the maximum permissible contact time in the metal melt, produces a metal strand with an approximately 6- to 10-fold total strand thickness. Here, the strand consists of the metal profile and crystals deposited thereon in a phase-boundary-free manner and molten material from the metal melt.